U0178: Perda de comunicação com o sensor I do sistema de retenção
O que fazer
The airbag warning light means the crash protection may not be working properly.
One question is worth asking before any part is bought: does your car actually have that sensor?
Cars are built on the same body in different specifications and for different markets — curtain airbags, knee airbags, rear pretensioners, pedestrian protection are all optional somewhere — and the airbag computer has to be told which of them your car has.
If that computer has ever been replaced, particularly with a second-hand one or after accident repair, it may be looking for a sensor your car never had. It reports the sensor as missing forever, and no amount of testing finds a fault, because there is nothing there to fail.
Here is the useful part: if a thorough search finds nothing, that is itself the answer. A sensor that is fitted but disconnected can be found with a meter in minutes; one that was never fitted cannot be found at all. At that point the right step is to check the car's original build specification — and correcting the coding is far cheaper than continuing to look.
If the sensor does exist, everything on the other pages in this family applies: mention any bumper, door, seat or trim work, and anything fitted after the car was built.
O que este código significa
A restraints system sensor has stopped being heard from. See U0170 for the one-versus-several rule and U0479 for the configuration argument, which is stronger for a lost-communication code than for any other kind.
The reason is simple and worth stating precisely: a module cannot tell the difference between a sensor that has gone quiet and a sensor that was never fitted. Both produce exactly this. So a vehicle coded for a higher specification than it was built to reports lost communication permanently, from the moment it is coded, and no test finds anything — because there is nothing to find.
That makes the search itself diagnostic, in a way it is not elsewhere. A sensor that exists but is unpowered or disconnected is found with a meter in minutes. A sensor that was never installed cannot be found at all. So an exhaustive search turning up nothing is evidence rather than failure, and the correct next step is to read the vehicle's build data rather than to keep looking.
Restraints configuration varies more than most, because it varies by market as well as by specification. Curtain airbags, knee airbags, rear pretensioners, pedestrian protection and rollover sensing are all options somewhere, and the restraints module has to be told which of them this vehicle has.
Three things put the wrong configuration into a vehicle:
- A replacement restraints module coded from a generic file rather than from the vehicle's own build record.
- A used module from a better-equipped car, which arrives carrying its old configuration.
- A module reprogrammed after accident repair from the wrong build data.
All three are coding corrections rather than repairs, and all three are far cheaper than the search that precedes them when nobody thinks to ask.
Causas prováveis
Comece aqui
- Módulo não codificado para o veículo · especializado
- Módulo usado bloqueado em outro veículo · especializado
- Conector corroído ou frouxo · fácil
- Sensor de impacto deslocado durante reparo de funilaria · moderado
Menos comum
- Chicote elétrico danificado · moderado
- Módulo do sistema de retenção com defeito · especializado
Sintomas
Componentes envolvidos
Informação, não instrução
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Antes de agir com base em qualquer orientação, peça a verificação de uma pessoa com formação técnica, seguindo o procedimento do próprio fabricante para o seu veículo. Nada aqui substitui esse procedimento.
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